Strand transposition



Jan. 28 1958 RINGLAND 2,821,641

STRAND TRANSPOSITION Filed April 16,1956

Bx c025 LEA/G TH United States Patent 2,821,641 STRAND TRAN SPOSITION William L. Ringland, West Allis, Wis., assignor to Allis- Chalmers Manufacturing Company, Milwaukee, Wis.

Application April 16, 1956, Serial No. 578,520 9 Claims. (Cl. 310-213) This invention relates generally to an electrical conductor, and more particularly to a transposed stranded conductor for windings of dynamoelectric machines.

The conductors forming the stator windings of large alternating current machines are disposed in slots of considerable depth formed in the stator core of the machines. Current flowing in these winding conductors produces a flux across the core slot and in the core end areas. This flux varies in density from the bottom to the top of the core slot and radially of the conductor in the core end area, the more dense flux being at the mouth of the slot and radially inward portion of the conductor in the end area. This flux, increasing from the bottom to the top of the conductor slot and cutting the conductor, produces unequal strand voltages which in turn cause eddy currents to flow and added heating of the conductor.

Conductors for windings for dynamoelectric machines have heretofore been constructed wherein the conductor is subdivided into a plurality of parallel connected transposed strands which are separately insulated to reduce the eddy currents and the losses which result from them.

Additionally, stranded or composite conductors having two rows of strands are commonly built with transposed strands arranged in rectangular form suitable for utilizing all the space of the rectangular slot of the dynamoelectric machine. The effectiveness of the strand transposition to eliminate eddy currents depends upon the arrangement of the various strands or how completely the positioning of the strands equalizes the nonuniform strand voltages caused by the nonuniform flux.

For example, one method of transposing the strands as they pass through the core slot is to transpose the strands uniformly through 360 degrees such that each strand occupies all core slot length. However for this method of transposition the strands at the opposite ends of the core are in the same relative position radially of the slot, and the strand voltages due to the variations in the end flux are not eliminated.

Transposing the conductor strands uniformly through 180 degrees such that the strand positions on opposite ends of the conductor are reversed equalizes strand voltages due to variations in the end flux, however, the strands do not occupy all strand positions for equal portions of the conductor length, and the strand voltages due to variations in the slot flux are not sufliciently equalized.

According to the present invention, the conductor strands arranged in two equal side by side rows are transposed in a novel manner by rotation through 540 degrees such that the strands occupy all strand positions for equal portions of the slot length and the strand positions at -opposite ends of the core are reversed. The strands by the present arrangement are transposed uniformly, but at a different rate in the first and fourth quarters of the conductor length than in the second and third quarters. By the present arrangement of conductor strands strand voltages due to variations both in the slot flux and the end flux are effectively equalized.

It is therefore an object of this invention to provide an improved stranded electrical conductor with transposed strands.

Another object of this invention is to provide an improved stranded electrical conductor for core windings of a dynamoelectric machine in which the strands are transposed to equalize strand voltages.

Another object of this invention is to provide an improved stranded electrical conductor in which the strands occupy each strand position for equal lengths and are reversed top to bottom at opposite ends of the conductor.

Other objects and advantages will be apparent from the following description taken in connection with the accompanying drawing, in which:

Fig. l is a schematic longitudinal view of a conductor illustrating the transposition of the conductor strands of the present invention;

Fig. 2 is a sectional view IIII of Fig. 1;

Fig. 3 is a sectional view of IIIIII of Fig. 1;

Fig. 4 is a sectional view IV-IV of Fig. 1;

Fig. 5 is a sectional view V-V of Fig. 1; and

Fig. 6 is another embodiment of the invention.

Referring more particularly to the drawing, the invention is illustrated as conductor 10 which is substantially rectangular in cross section and inserted into an axial slot 11 in the stator core 12 of a dynamoelectric machine to form a portion of a winding for the dynamoelectric machine. Two conductors 10 are shown in each slot, and the core slot length extends between section lines IIII and V-V as shown in Fig. 1.

Conductor It) comprises a plurality of substantially rectangular strands, identified in the drawing as a through 1'. Strands a through j are connected in parallel to form conductor 10.

The strands are arranged in two rows or columns, side by side, of an equal number of strands. Strands a through 1' are insulated from each other by insulation (not shown) around each strand and from the core slot and adjacent conductor by insulation 14.

Fig. 1 illustrates the transposition of the strands a through i. The first row of strands is shown as solid lines, and the second row of strands is shown as dotted lines. The second row is offset slightly to more clearly illustrate the transposition of strands. Thus, section IIII shown in Fig. 2 illustrates the relative strand position at one end of the conductor as the conductor enters the core slot.

In distributing the conductor along the core slot length, the conductor strands are transposed uniformly by rotationto occupy all slot positions. This transposition is illustrated in Fig. l for a clockwise rotation of strands a through 1' in that conductor a follows conductor b from the top to the bottom of the core slot, and continues around to the top again. Rotation of the strands may, of course, be either clockwise or counterclockwise.

In distributing the conductor along the first quarter of the conductor length, the strands are transposed by rotation to occupy slot positions through degrees. The relative strand position at the end of the first quarter length of the conductor is illustrated in Fig. 3 which is a view along section IIIlII of Fig. 1. Thus, along the first quarter of the slot length the strands are transposed uniformly through 180 degrees, and all of the strands occupy half of the slot positions for equal portions of that quarter of conductor length.

Over the second and third quarter of the conductor of the conductor along section produce a voltage difference length, or over half of the conductor length, strands a through i are again transposed uniformly by rotation through 180 degrees but at half of the rate at which the strands were transposed over the first quarter of the length of the conductor. The relative strand position at the end of three-quarters of the conductor length is illustrated in Fig. 4 which is a view along section IV-IV of Fig. l. The relative position of the strands at this point is the same as the relative position of the strands as they entered the core slot. In other words, the total transposition of the conductor strands after threequarters of the conductor length has been 360 degrees.

Over the second and third quarters, or half, of the conductor length all of the strands again occupy half of the slot positions through 180 degrees for equal portions of the half of conductor length. However, the slot positions occupied by the strands along the second and third quarters of the conductor length are positions not occupied by the particular strands along the first quarter of conductor length. Also, the transposition through 180 degrees in the second and third quarter is over twice as long of a portion of the conductor length as the transposition through 180 degrees in the first and fourth quarters.

Along the fourth quarter of the conductor length, strands a through 1' are again transposed by rotation uniformly through 180 degrees and at the same rate at which they were transposed over the first quarter of the length of the conductor. The relative strand position at the end of the conductor is illustrated in Fig. 5 which is a view along section V-Vof Fig. 1. At this point, each strand has been transposed through 540 degrees. The relative slot positions occupied by the particular strands along the fourth quarter of the conductor length are the same slot positions occupied by the particular strands along over the first quarter of the slot length.

It will now be seen that the strands are transposed through 180 degrees in each of the first and fourth quarters of the conductor length and that the strands are also transposed through 180 degrees over the combined second and third quarters of the conductor length. Also, since the strand transposition is uniform through each portion of the conductor length, and since each strand occupies half of the strand positions during the first and fourth quarters of the conductor length and each strand occupies the other half of the strand positions during the second and third quarters of the conductor length, each strand has occupied every slot position for an equal portion of the length of the conductor.

It will also be seen that as each strand has been transposed through three 180 degree transpositions, or a total of 540 degrees, the relative position of the strands is reversed top to bottom, or rotated relatively 180 degrees, at opposite ends of the conductor.

When current flows through conductor 1%, fiux caused by this current will vary in density from the bottom of the slot to the top. This difierence in flux density will between conductor strands. By the above described transposition conductor comprises a plurality of strands with each strand occupying each slot position for an equal portion of the conductor length. Because each strand occupies each slot position for an equal portion of the conductor length, the strand voltages due to varying slot flux are substantially equalized.

Also, by the above described transposition conductor 10 comprises a plurality of strands with each strand occupying reversed top to bottom conductor positions, that is, relative positions rotated through 180 degrees at opposite ends of the conductor. Because each strand occupies a relative position rotated through 180 degrees at opposite ends of the conductor, strand voltages due to radially varying end flux are etfectively canceled.

Fig. 6 illustrates another embodiment of the invention in which cooling tubes are positioned in the slot in substantially direct contact with the conductors. For

this embodiment, conductors a through I are rotated ii the same manner as described above.

Although but two embodiments of this invention have been shown and described, it is understood that various changes and modifications can be made therein without departing from the spirit of this invention or from the scope of the appended claims.

It is claimed and desired to secure by Letters Patent:

1. In a dynamoelectric machine having a core with a slot, a conductor disposed in said slot, said conductor comprising a plurality of conductor strands .arranged in two rows having an equal number of strands insaid rows, said strands being transposed by rotation to occupy each slot position in said rows for substantiallyequal portions of said slot length and to occupy reversed top to bottom slot positions at opposite ends of said slot.

2. In a dynamoelectric machine having a core with a slot, a conductor disposed in said slot, said conductor comprising a plurality of conductor strands arranged in two side by side rows'having an equal number of strands in said rows, said strands being'transp'osed by rotation to occupy each slot position in said rows for substantially equal portions of said slot length and to occupy relative slotpositious rotated 180 degrees at opposite ends of said slot.

3. In a dynamoelectric machine having a core with a slot, a conductor disposed in said slot, said conductor comprising a plurality of conductor strands arranged in two rows having an equal number of strands, said strands being transposed uniformly by rotation through 180 degrees over the first quarter of length of said slot, through 180 degrees over thesecond and third quarters of the length of said slot, and through 180 degrees over the fourth quarter of the length of said slot.

4. In a dynamoelectric machine, a core having an axial slot, an electrical conductor in said slot comprising a plurality of strands arranged in two columns having an equal number of strands, said strands being transposed by rotation to occupy each strand position in both of said columns for substantially equal lengths of saidrslot and to occupy inverse top and bottom positions at opposite ends of said slot, transpositioned crossovers between said column being at a rate in-portions of said slot length which is twice the rate of said transpositioned crossovers in the remainder of said slot lengt 5. In a dynamoelectric machine, a core havingan axial slot, an electrical conductor in said slot comprising a plurality of strands arranged in'two columns having an equal number of strands, said strands being transposed uniformly by rotation through 180 degrees over a first portion of said slot length, through l-degrees over a second portion of said slot length, through degrees over a third portion of said slot length, said transpositoned crossovers in said second portion being double spaced along said slot length with respect to said'transposition crossovers in said first and-said third portions.

- 6. In a dynamoelectricmachine, a core'having an axial slot, an electrical conductor in said slot comprising a plurality of strands arranged in two columns having an equal number of strands being transposed uniformly by rotation through 180 degrees over each ofthree portons of said slot length, saidtransposition crossovers in the middle portion of said three portions being double spaced with respect to said transpositioned crossovers in said other two portions.

7. In a dynamoelectric machine, a core having an axial slot, an electrical conductor in saidslot comprising a plurality of strands arranged in two columns'having an equal number of strands, said strands being transposed uniformly by rotation through 180 degreesover a first portion of said slot length, through 180 degrees over-a second portion of-said slot length, and through 180 degrees over a third portionofsaidslot'length, said-first and said third portions extending through one-quarter of the length of said core slot and said second portion being between said first and said third portions.

8. In a dynamoelectric machine, a core having an axial slot, an electrical conductor in said slot comprising a plurality of strands arranged in two columns having an equal number of strands, said strands being transposed uniformly by rotation through 180 degrees over each of three portions of said slot length, said strands occupying each strand position for substantially equal portions of said slot length.

9. In a dynamoelectric machine, a core having an axial slot, an electrical conductor in said slot comprising a plurality of strands arranged in two columns, said strands being transposed by rotation to occupy each slot position in said columns for substantially equal portions of said slot length and to occupy relative strand positions in said slot rotated 180 degrees at opposite ends of said slot.

References Cited in the file of this patent UNITED STATES PATENTS 1,144,252 Roebel June 22, 1915 FOREIGN PATENTS 365,512 Great Britain Jan. 13, 1932 457,415 France July 10, 1913 

